Digital camera technology is being used in an increasing variety of mass-produced applications, and in increasing production volumes. For example, miniature fixed-focus digital camera modules are being incorporated into consumer products such as portable telephones and personal digital assistants (PDA's). Given the new high volume applications for digital camera modules, it is desirable to reduce their per unit material and assembly costs.
Digital camera modules generally include a lens for focusing incoming light onto an image sensor that detects an image and converts it into an electrical signal representation. An image processor is employed to further manipulate the image signal into an image of a suitable quality for output. Digital camera modules also typically include a chassis and enclosure for mounting the various electronic and optical components and for protecting the components from particulate and spurious light contamination.
Modern digital camera modules are expected to provide high-quality imaging at low cost. Notwithstanding signal processing techniques, image quality fundamentally depends on the camera's optics. In fixed-focus camera modules, the focus is often set as part of the assembly process. Conventional assembly processes for digital camera modules tend to be labor-intensive. In particular, the focusing is often a manual operation in which an operator sets and secures the focus of each individual unit. Typically, setting the focus requires high-precision positioning of the camera's lens relative to the image sensor.
Because traditional focusing processes are manual operations, and because human operators cannot reliably achieve a sufficient focus without mechanical assistance, conventional camera modules typically include high-precision structural features that facilitate setting the proper focus, such as a lens assembly that attaches to the camera housing with screw threads. The threaded attachment provides a mechanism for positioning the focal point on the image sensor, and maintains planarity between the lens and image sensor. During assembly of a conventional digital camera module, an operator typically threads the lens assembly onto the camera housing until a proper focus is achieved. Next, the operator fixes the threaded lens assembly positioning with a drop of adhesive, for example. Therefore, the screw threads on the lens assembly and camera housing provide a mechanism for achieving a high accuracy/high precision positioning of the lens and image sensor without the use of high precision assembly instruments.
As mass-produced products, digital camera modules are preferably constructed from low-cost materials whenever possible. The use of built-in structural features, such as screw threads, for establishing a proper focus for each manufactured digital camera module, limits the ability to use low cost construction materials. Only certain types of materials can support machining and/or high precision molding, and such materials are typically more expensive than the materials that are unable to support such processes. Also, it is desirable to minimize per unit costs associated with the assembly process. Creating high-precision features typically requires machining the parts and/or molding the parts with high precision. For parts having machined features, the process of machining adds costs to the parts. Moreover, particulate residue from the machining process can remain on the parts and can potentially settle on the image sensor, thereby partially obstructing it. For parts molded with high precision, materials of relatively high cost are typically required, as compared to materials for low-precision molded parts.
An alternative solution to high-precision lens/image sensor placement is the use of lens materials that permit high-tolerance placement of the lens and image sensor. However, such materials are costly compared to conventional lens materials.